The purpose of this study was to investigate the effects of plyometric and weight training protocols on the mechanical properties of muscle-tendon complex and muscle activities and performances during jumping. Ss (N = 10) completed 12 weeks (4 days/week) of a unilateral training program for plantar flexors. Plyometric training was performed on one side (hopping and drop jump using 40% of 1 RM) and weight training on the other (80% of 1 RM). Tendon stiffness was measured during isometric plantar flexion. Three kinds of unilateral jump heights using only the ankle joint (squat jump; countermovement jump; drop jump) on a sledge apparatus were measured. During jumping, electromyographic activities were recorded from the plantar flexors and the tibial anterior muscle. Joint stiffness was calculated as the change in joint torque divided by the change in ankle angle during the eccentric phase of a drop jump.

Tendon stiffness increased significantly for the weight-training exercised joint, but not for the ankle undergoing plyometric training. On the other hand, joint stiffness increased significantly with plyometric training, but not for weight training. Whereas plyometric training increased significantly the jump heights of the squat jump, countermovement jump, and drop jump, weight training only increased the squat jump height. The relative increases in jump heights were significantly greater for plyometric training than for weight training. There were no significant differences between the two training forms in the changes in the electromyographic activities of measured muscles during jumping. Performance changes resulted from structural/mechanical rather than metabolic changes in the joint and its musculature.

Implication. Jump performance gains after plyometric training can be attributed to changes in the mechanical properties of muscle-tendon complex, rather than to the muscle activation factors.

[This study reinforces the recommendation that explosive activities can only be stimulated by explosive movements and that muscle activation exercises, such as strength training, do not contribute to enhancing high-velocity movements. High rates of movement in a large part depend on factors such as elastic energy rather than metabolic energy.]